Ammonium perchlorate is produced from sodium perchlorate by mixing sodium perchlorate solution with ammonium chloride, heating the solution mixture to about 100° C. and then cooling it at a controlled rate to achieve the desired particle size distribution. Ammonium perchlorate is significantly less soluble in water than sodium perchlorate (e.g., 115 g/l vs. 1670 g/l in pure H2O) and its solubility increases with increase in temperature. On cooling the solution mixture, ammonium perchlorate precipitates out of the solution mixture, producing slurry consisting of ammonium perchlorate crystals in a mother liquor mostly comprised of sodium chloride. Controlled cooling and/or mechanical rounding of crystals are done to produce crystals meeting to the particle size distribution required in the final product. The ammonium perchlorate crystals are separated from the mother liquor, washed with water to remove sodium and chloride contaminants, and dried to produce the final product.
The mother liquor is mostly a sodium chloride solution in this process with some dissolved perchlorates. It is evaporated in a salt evaporator, which is typically an expensive piece of equipment built with exotic materials to avoid serious chloride corrosion issues. Such equipment is required to produce salt which is recycled back to the front end of the closed process loop for producing sodium perchlorate electrochemically which is then used for producing more ammonium perchlorate as noted above.
There are many issues with the chloride based processes. For example, the process requires salt evaporators built with exotic and expensive material(s) to produce salt. Being a chloride-based process, equipment corrosion is a serious plant-wide issue, which not only requires the use of process equipment built from the salt-resistant material(s) but also to keep the plant equipment to be well maintained at all times, costing resources and money. The by-product of the process, sodium chloride, is contaminated with perchlorate and if it is not recycled, which would be the case if the purchased sodium perchlorate is used for ammonium perchlorate production instead of the site-produced sodium perchlorate, its disposal is a serious issue, a source of liability instead of revenue. Another issue with the process is that the ammonium perchlorate crystals are separated from a chloride-rich solution. To meet the chloride specification of the final product, it requires thorough washing of the ammonium perchlorate cake prior to its drying, adding more steps to the production process, making it complex and difficult to control, and at times requiring re-dissolving and re-crystallization of the final product to achieve the desired chloride specification in the final product.
In some operations, ammonium sulfate is used, instead of ammonium chloride, to produce ammonium perchlorate from sodium perchlorate. It surely helps the corrosion issue, but does not help the perchlorate-contaminated by-product (sodium sulfate) disposal issue. In this case also, like the process described earlier with ammonium chloride, the by-product does not contribute to the revenue; instead it consumes revenue.